Much work has been done with a goal of creating small fuel particles that create a homogeneous mixture that is more readily combusted in an internal combustion engine. One area that is being actively investigated is that of Radical Activated Combustion (RAC). In this configuration, fuel free radicals are introduced into the combustion chamber to enhance combustion. Successful demonstration of such a condition in a two cycle engine has been demonstrated. The two cycle cylinder retains free radicals from the previous combustion cycle and combustion occurs without a spark plug as an ignition source. The cylinder is in effect full of many thousands of “spark plugs” that initiate combustion in the cylinder.
Another engine type is referred to as a Homogeneous Charge Compression Ignition Engine (HCCI). The engine attempts to create a diesel like configuration with a similar homogeneous gasoline mixture. The means of initiating combustion throughout the complete range of driving conditions from low load to high load remains a problem with this engine.
Soot formation in a diesel engine primarily occurs at the first stage of introduction of fuel into the hot compressed air in the cylinder. Diesel engine development activities to eliminate soot formation have been centered on producing small fuel particles by increasing fuel injector pressure to extremely high pressure. The resulting fuel supply system in the modern diesel engine can be as high as 35% of the total cost of the engine proper. Only incremental results have been achieved and modern “clean” diesels require a particulate trap and an oxide of nitrogen trap that require regeneration. Government mandated emission requirements continue to be increasingly more stringent.